This is a contract for the planning, execution, and analysis of a clinical trial to test the efficacy of a cystine-depleting drug as therapy for nephropathic cystinosis. In the first year of the contract, in vitro and in vivo and in vivo investigations will determine which cystine-depleting drug offers the best prospect as an alternative to cysteamine as an agent for arresting the kidney damage characteristic of nephropathic cystinosis. After the choice of drug and its dosage is determined, a protocol will be drafted for randomly allocating a total of at least 60 cystinosis patients to receive either cysteamine or the test drug. In ensuing years patients will be recruited and followed-up at regular intervals to measure renal function, growth, compliance to protocol, and other clinical indices. Data are to be collected, edited, and maintained on an accessible computer file, which is to be remanded to NICHD at the contract's conclusion. In the final year, analysis, to be carried out at the direction of NICHD, will be to determine if the therapeutic effect of the test drug is better than that of cysteamine.